Power output tube bias arrangement



July 2s, 1936. J. s) TARRETT .Y 2,048,758

POWER OUTPUT-TUBE BIAS ARRANGEMENT Filed April 7, 1933 FiF/9000659 INVENTOR JOHN S. STARRETT ATTORNIEY,

Patented july 28, 1936 POWER OUTPUT TUBE BIAS ARRANGEIWENTA 7.1 .lohn S. Starrett, Livingston, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application April 7, 1933, Serial No. 664,969

11 Claims.

My present arangement relates generally to circuits for providing bias for power tubes, and more specifically to an improved biasing circuit of this type wherein oscillator voltage is rectiiied and utilized for providing the bias for the power output tube of a radio receiver.

- In using an electron discharge tube as a power output device, it is well known that when a selfbiasing resistor is employed, precautions must 1o be taken to prevent undue coupling between the plate and grid circuits. Pulses of current in the plate circuit tend to alter the bias on the grid since the resistor is common to both. To minimize the degeneration and distortion caused by is "such coupling, a large capacity is usually shunted across the resistor to give this circuit element a time constant sufficiently large so that essentially constant bias is obtained. In larger power tubes (such as the 2A3) where the peak swings of current are large compared to the steady or no signal plate current, and also under class A prime conditions, it is evident that such peaksrcan be sustained for but a very short interval due to the physical limitations of this network, and hence the maximum power output can be secured only momentarily,

The use of a iixed bias from the bleeder of the receiver would probably result in more satisfactory operation in this respect, but would impose th@ necessity of providing for quite heavy bleeder currents since the peak current required by the power tubes is large compared to the current required by the other tubes in the receiver. It is, also, apparent that in receivers of the automotive V or direct current types whereV the total supply voltage is limited, the necessity of using part of this for bias limits the power output which may be obtained. In the case of the type 48 tube,

two such tubes in push-pullprovide an output of about 3.5 watts when used with 95 volts on the plate, while at 125 volts,v 5.5 watts is obtainable.

From the above considerations it is evident that it would be desirable in many cases to have available an independent source of bias voltage. While thismight be obtained from C batteries, the additional space required and other considerations have led receiver designers in the past to look with disfavor upon the inclusion of batteriesin an all-electric unit.

Now, I have discovered a novel method of, and

devised means for, solving the aforementioned.

problems. According to the present invention there is provided a method of obtaining a source oi bias for the power stage of a receiver which is essentially independent of fluctuations such as ordinarily experienced when bleeder, or selfbiased, circuits are used. The bias isI obtained from the rectification of voltages generated within the receiver, whether of beating frequency or, not. v Y 5 It may be stated that it is an important object. of my present invention to provide an arrange-` ment for supplying proper negative operating bias` for the power output tubes of a radio receiver, as.. for example oi the superheterodyne type, by recl0 tifying a locally generated oscillation voltage, and applying the rectified voltage vbetween the input electrodes of such power tubes. Y

In applying the present invention to a super- I heterodyne receiver it has been found convenient l5 and advantageous to embody the local oscillator and rectifier of the beating voltage in a single electrical instrumentality. To accomplish this, advantage has been taken of the fact that there exists an electron discharge tube of the type 2.9 known as a duplex diode triode. It may, there-1 fore, be stated that it is another important object of the present invention to provide a supere, heterodyne receiver with a local oscillator circuit embodying a single tube functioning asa triode25, oscillator and diode rectifier, the rectiiier `func. tioning to rectify the voltage produced byV the triode oscillator, and the rectiedvoltage being, applied as a negative bias potential between thelinput electrodes of the power output tube,V ongftubes, of the receiver.

Still other objects of the present invention are, to improve generally the simplicity and eiiiciency; of superhetero-dyne receivers, and to provide particularly a receiver ofthis -type which isA not onlyugg reliable in operation but economically manufacg, tured and assembled. A

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims, the invention 40* itself, however, as to both its organization andf method of operation will best be Aunderstood byreference to the following description taken in, connection with the drawing in which I have indicated diagrammatically an arrangement whereby 45 my invention may be carried into' effect.

Referring now to the accompanyingdrawing, wherein thesingle gure diagrammatically shows a superheterodyne receiver ofja'conventional type, I

it will be noted that the iirstA detector tube l is 50 of the radio frequency pentode type. In this type of tube' the suppressor grid, at cathode-pjotential, is disposed between the positive screen4 grid and the more positive ano-de. The source of positive potential for tliescreen grid-Of tube l55'`j is designated by the symbol S1, and the source of the more positive potential for the anode of tube I is designated by the symbol P1. A negative bias is supplied to the co-ntrol electrode of tube I from a source G (not shown), the negative terminal of this source being connected to the control electrode of tube I through a path which includes the resistor R1, and the coil L.

Signal Vvenergyis impressed upon the tunable input circuit of tube Il through the coupling transformer M, and the variable tuning condenser C4 is connected in the usual manner across the coil L. The grounded side of the condenser C4 is connected to the low potential side of the coil L through a direct current blocking condenser C7.

The anode circuit of the tube I includes therein a coil L5 shunted by a fixed condenser Cs. The high potential side of the network. Ls--Ca is connected to ground through a radio frequency bypass condenser 2. The network L5-C is maintained Xedly resonant to the operating intermediate frequency, and the intermediate frequency energy -derived fromr this network is impressed upon a. succeeding intermediate frequency amplifier. This amplifier is omitted since its construction is well known to. those skilled in the art. Additionally, the second detector which usually follows such an amplifier is omitted, and in order to preserve. simplicity of description, there is only shown the input transformer connected to. the power output tubes 3, 4.

The audio frequency input transformer M1 has its primary coil L6 arranged for connection to the output circuit of the second detector, while the secondary coil L7 has one side thereof connected to the control electrode of tube 3, and its other side. connected .to the con-trol electrode of tube 4. Both cathodes of tubes 3 and 4 are grounded. The'anode of Vtube 3 is connected to one side of the output.. transformer primary coil Ls, while the anode of tube` 4 is connected to the opposite side of this coil. The secondary coil of the power output transformer is arranged for `connection toA a 'reproducen not shown, or it may even be connected to additional stages of` audio frequency amplification.

The4 anodes of tubes 3 and 4 are energized from a source of positive potential P2, not shown, and the lead' from the positive terminal of this source toi the anodesof' tubes 3 .and 4 is connected to the midpoint of the coil Ls. Themidpoint of the coil L7 is connected bya lead 5' toa negative biasing arrangement to be hereinafter described.

' Thev local oscillator'ci-rcuit of the superheterodyne receiver sho-wn comprises the tube 6, this tubel being of the duplexV diode triode type described and claimed by Terry M. Shrader in application Serial No. 622,140, iiledJuly 12, 1932. It is'not believed necessary to go into 'details with regard` to the description of this type of tube since the aforementioned Shrader application describes the construction in detail. It is believed sufficient to point out that the tubeV 6, which may be ofA the 55,; or' 85ty'pe, is a tube consisting of two diodes aand' a triod'ein a single envelope. The two diodes andthe triode are independent of each other,"except for a commbn cathode sleeve I which'has one emitting surface for the diodes and anotherfor the triode.

Within the common envelope of the tube are provided theY auxiliary diode anodes 8 and 8', while the triode portionof the tube comprises the mainanodeV 9 and the usual control grid ID disposedbetween the cathode 'I andthe anode 9..

The two diode plates 8 and 8 are placed around a portion of the emitting surface of the cathode 'I which is independent of the portion of the emitting surface around which the grid I0 and anode 9 are disposed. In other words, the diode anodes 8 and 8' are outside the electron stream passing through the grid Ill tothe anode 9.

The triode portion of the tube 6 is utilized as the local oscillator of the receiver, while the diode portion of the tube is Vused as the rectifier for the oscillator beating voltage, the rectified voltage to be utilized as the negative biasing voltage for the power output tubes. The coil L4 is shown coupled to the conventional oscillator coil assembly and rectified current flows in the resistor R. The conventional oscillator coil assembly cornprises the feed-back coil L3, connected between the anode 9 and the positive terminal of the anode potential source P3 (not shown).

A radio frequency by-pass condenser I I is connected between ground and one side of the feedback coil L3. The coil L2 is disposed in the circuit of the cathode of the rst detector tube I, the groundedA side of the coil L2 including a resistor R2 shunted by a radio frequency by-pass condenser I2.

Both coils L3 and L2 are coupled to each other and, to the coil L1, the latter coil being connected,.on one side thereof, to the grid IIJ through the condenser` C6, there being shunted across the coil L1 a xed condenser C2 and the variable condenser C3. A lead I 3 is connected between a point' intermediate condensers C2 and C3 and thez grounded side of the cathode 7, and the resistor R3 is connected between the grid IIJ and grounded side of cathode l.

the cathode I and its other side connected to the lead 5.

'Ihe coil L4 has one side thereof connected to the diode anodes 8 and 8', the both anodes being tied together,A while the opposite side of the coil is connected, through a lead I 4, to ground through a condenser C1, a radio frequency by-pass con-l for simultaneous adjustment in anywell known manner, and this. is designated by the dotted line I5. The condenser C is a by-pass'for the beating frequency, while the condenser C1 serves The bias resistor R has oneV side thereof connected to the grounded sideof to keep this voltage from the power tube grids;` The resistor R should be sufficiently large so that no appreciable load is-put on the oscillator. The power tube grids are connected to the nega-A tive end of .the resistor R.

The signal input network preceding the first detectorvtube I may include one or more tuned' radioffrequency amplier stages, if desired; Also,

clearly understood from the following explana-` tion:

The locally produced oscillations' are impressed upon the cathode circuit of the rst detector, or frequency changer tube, and the local-oscillations are, of course, produced by feeding radio fre quency energyfrom the anode circuit of tube 6, through coils L3 and L1, to thesgrid circuitl there` of. In other words, thetriode portion 1, I0 and' 9 75;'

0f tube "5, and its 'associated coils La and L1', function as a triode oscillaton The two diode an- Odes 8 and 8 tied together, and their associated lC2 is part of the tank circuit, or tuning capacity. Y The negative biasing voltage obtained from the oscillator would vary considerablywith frequency if the ordinary coil and condenser connections were used. The combination of C2 and C3 indi-l cates a means of keeping this voltage constant.A

The cathode is connected to a variable potential point between these condensers. varied from maximum to minimum capacity the normal increase in voltage with increase in frequency is reduced due to the increased'impedance of. C3 as compared to C2. Thus by proper proportioning of C2 and C3 quite constant voltage `will be introduced into coil L4. Other networks of capacity and inductance' might be employed in place of that shown to secure the constant voltage condition.

An alternative arrangement to accomplish the aforementioned result would be to employ an extra winding on the power transformer of the receiver, with a small rectifier tube connected to rectify the 60 cycle alternating current voltage. With such a circuit however the filter would need to be very effective because of the possibility of introducing hum, and would be relatively more expensive and bulky, than the filter required for radio frequencies. An extra tube would also be required if 60 cycles were used, while in the radiofrequency energy only the usual number of tubes is needed.

While I have indicated and described one system for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention as set forth in the appended claims. For example, the invention is applicable to a combined detector-oscillator, that is an autodvne first detector circuit, instead of independent oscillator and detector tube circuits.

What I claim is:

l. A method of biasing an input electrode of a power output tube of a radio receiver which includes the steps of detecting signal energy for subsequent amplification by said power tube, simultaneously producing local oscillation energy of a frequency of the order of the signal frequency, rectifying said oscillation energy, and applying said rectified energy as a biasing potenal for said input electrode.

2. In a superheterodyne receiver, provided with a first detector and at least one audio frequency amplifier tube, and a local oscillator circuit, a rectifier network operatively associated with said local oscillator for rectifying the oscillator beating voltage, and means for applying said rectified voltage to an input electrode of said amplifier tube as a bias therefor.

3. *In a superheterodyne receiver', provided with a rst detector and at least one audio frequency amplifier tube, and Va local oscillator circuit, aV diode rectifier network operatively 'associated with said'local oscillator Y,for rectifying the oscillator beating voltage, and means for applying said rectified voltage to 'aninputfel'ectrode of said amplifier tube asv a bias therefor.

4; In a superheterodyne receiver, provided with a rstdetector and at least one audio frequency l amplifier tube, anda local oscillator circuit, means for tuning the oscillator circuit over a frequency range, av rectifier network operatively associated with'said local oscillator for rectifying the oscillator beating voltage, means in the os'f1 cillator circuit to maintain the rectified voltage constant, and means for applying said rectified voltage `to the grid of'said amplifiertube as a bias therefor. c .Y f

' 5. In combination with a superheterodyne receiver of the type including a frequency changer network, a succeeding audio frequency'amplifier tube, and a. local 'oscillator circuit, Va diode rectifier circuit coupled to said local ,oscillator circuit to derive *oscillator energy therefrom, said 25 rectifierr'circuit including an. impedance for developing a direct current potential, and a conductive connection between the negative side of said impedance and an input electrode of said amplier tube.

6. In combination with a superheterodyne receiver of the type including a frequency changer network, a succeeding audio frequency amplifier tube, and a local oscillator circuit, a diode rectifier circuit coupled to said local oscillator circuit to derive oscillator energy therefrom, said rectifier circuit including an impedance for developing a direct current potential, anda conductive connection between the negative side of said impedance and an input electrode of said amplilier tube for impressing said potential on the said electrode, said local oscillator circuit and diode rectifier circuit having their electrodes disposed within a common tube envelope.

'7. In combination with a superheterodyne receiver of the type including'a frequency changer network, a succeeding audio frequency amplifier tube, and a local oscillator circuit, a diode rectifier circuit coupled to said local oscillator circuit to derive oscillator energy therefrom, said rectifier circuit including an impedance for developing a direct current potential, and a conductive connection between the negative side of said impedance and an input electrode of said amplifier tube for impressing said potential on the said electrode, said local oscillator and diode rectifier circuits having their electrodes disposed within a common tube envelope, the cathode of said common tube being common to the oscillator and rectifier electrodes.

8. In combination with a superheterodyne receiver of the type including a frequency changer network, a succeeding audio frequency amplifier tube, and a local oscillator circuit, a diode rectifier circuit coupled to said local oscillator circuit 6 to derive oscillator energy therefrom, said rectifier circuit including an impedance for developing a direct current potential, and a conductive connection between the negative side of said imped. ance and an input electrode of said amplier 7 tube for impressing said potential on the said electrode, said local oscillator and diode rectifier circuits having their electrodes disposed within a common tube envelope, the cathode of said common tube being common to the oscillator and 7 independent triode and diode sections, ycircuits associated with said triode section` for providing a triode oscillator circuit, circuits associated with said diode section, said diode circuits being kcoupled With Asaid, oscillator circuits, providing a diode recti-er circuit for thelocally produced oscillation energy, and a conductive connection for applying the rectified energy as a negative i bias for Vthe grids of said push pull connected tubes. l l i 10. In combination with la. superheterodyne receiver 4of the type including a frequency changer network, a succeeding audio frequency amplier tube, and a local oscillator circuit, a diode recti-V er circuit coupled to said local oscillator circuit to derive oscillator energy therefrom, saidrectifier circuit including an impedance for developing a direct current potential, a-conductive connecgtion between the negative side-of saidA impedance and an input electrode. of said amplier tube, means'for tuning the frequency changer network through a dsired'sign'al frequency range, means for tuning the local oscillator circuitfthrough a rangeY of frequencies differing from-the signal,

frequencies -by the operating intermediate frequencyfandhadditionalmeansiin the local oscil'-v lator-vcircuitfor.maintaining the said' direct current potential constant-in value asthe oscillator tuning means is varied,

I 11, AIrl-combination withasuperhetero'dyne receiverofthe type including a frequency Vchanger network, va Vsucceeding audio frequencyy amplifier tube, and alocal oscillator circuit, a diode recti-1 fier Vcircuit-coupled tosaid.- local. oscillator-l. circuit to deriveoscillator.energy-therefrom, said rectier circuit including an impedance for developing adirect current potential, and a conductive connection between the negative side of said im,

pedance and anv input electrode of said ampli'er tube, saidlocal oscillator circuit and diode rectifier circuithaving their lelectrodes disposed Within a common' tube-4 envelope, means for tuning the,V frequency changer network through a desired signalfrequency range, means for tuning. the local oscillator circuit-through va range of freq'uencies diifering" from 'the signal frequencies by the operating intermediatefrequency,v and-additional "means in the local oscillator circuit'forV maintaining the said'direct current potential constant in value as the oscillator tuning means is varied.V

'JOHN S. 'STARRETT 

